1. Field of the Invention
This invention relates to a process for preparation of mica-containing ceramic composite having low thermal expansion property, high heat-resistance, high mechanical strength, excellent electric insulation, and being capable of machining work, hence being useful as heat-resistant and insulating support members for vehicles and rolling stocks, arc-extinguishing members, heat-insulating members, etc., and other structural members for apparatuses and appliances in the fields of electric machinery, electronic machinery, industrial machinery, and so forth.
2. Discussion of Background
As a process for preparing a mica-containing ceramic composite which is similar to the process of the present invention and capable of being machined, there has so far been known one, as taught in Japanese Patent Publication No. 9614/1968, in which a mica-glass series material is produced by charging a mixture of mica powder and glass powder into a metal mold, and heating the mixture material to a temperature, at which the glass powder becomes molten, while simultaneously pressing the mixed material. This mica-glass series material is excellent in its electric insulation and dimensional stability, and capable of being processed into articles of various configurations owing to its good machinability, hence it has so far been used, in particular, as a heat-resistant electric insulators.
However, since this material has a large thermal expansion coefficient, it is apt to readily bring about cracks, etc., under the conditions such as abrupt heating and cooling, while it is being used. In particular, there tends to readily take place such an occasion, in which the mechanical strength of the material decreases to make it difficult to use the same any longer.
Further, when mica and borosilicate lead glass are made the constituent components (vide: "Glass Handbook" compiled by Sakuhana et al., published from Asakura Shoten (1982)), the thermal expansion coefficient of the material is as large as 10.times.10.sup.-6 to 12.times.10.sup.-6 /.degree.C., and its heat-shock temperature difference (.DELTA.T) is also as low as 180.degree. C. or so. Moreover, since borosilicate glass is a kind of low melting point glass, when it is used as a matrix, its heat deformation temperature (the minimum temperature, at which the material brings about blister), is mostly 500.degree. C. or so. Accordingly, the conditions for its use are limited.
The present inventors have already found out the process for preparing the mica-containing ceramic composite material having a low expansion property, for which they have filed a patent application (Japanese Unexamined Patent Publication No. 50365/1988).